Had another meeting with the local planning officer last week. We thought it was about time to check they were supportive of our plans in general, and wanted to ask specifically how they might feel about a green-roofed extension.
There was a bit of humming and hawing, with the uncertainty based on the fact that externally insulating the bungalow with straw would turn it into a rendered bungalow surrounded by rows of near-cloned brick bungalows. But they understood and seemed impressed by the reasoning behind the project (to bring a cold and damp bungalow up to at least level 5 of the Code for Sustainable Homes, making it warm, dry, cosy and healthy using the most sustainable materials we can). However, ultimately they appeared to be convinced that our compromise of leaving the projection at the front of the bungalow as brick and internally insulating that section was acceptable and enough to visually tie the building in to the rest of the street. Internally insulating is not ideal as there is more potential for condensation problems where the insulation meets the cold-hard surface of the external wall in a way which is not an issue with breathable external insulation - more on this in the blog soon.
General guidelines for extensions encourage them to be built using materials that match the existing structure, or at least have the same roof covering. Concrete tiles that match the existing roof can only be used on a roof slope higher than 22.5 degrees from horizontal, which would mean a very high and dominating roof on the extension (we also want to avoid concrete anywhere in the build due its incredibly high embodied energy, associated carbon emission and pollution produced during its production). There are different tiles that would allow a lower roof pitch, but these are a different colour and shape. The planning officer I spoke to was really helpful. She said saw no difference between using different tiles and a sedum roof, and thought it would be acceptable, but wanted to check with her manager. Later in the day she phoned having conferred with him and said they both agreed that a sedum roof should be acceptable, and that the wrap should be as well provided we do leave that front bedroom as brick. Yaay! This is no guarantee of getting planning permission, and once we actually apply the planning officers will come out and do a site visit, but it is very encouraging.
The advantage of a sedum roof over a grass roof is that it is more self-maintaining and doesn't have the same potential for becoming massively overgrown, which is the kind of thing that can upset some people with green roofs. Here's some examples via an image search: sedum roof examples.